The Nuclear Decommissioning Authority

The plans show how radioactive waste is to be removed from two underground facilities – a vertical shaft 65 metres deep and a nearby vault set nine metres into the ground – as part of the closure of the Dounreay site. 

The water-filled shaft and silo were once used for radioactive waste from some of Britain's earliest experiments with nuclear energy. 

Their clean-out is a key part of the site closure contract awarded by the NDA to the Babcock Dounreay Partnership (BDP) earlier this year. 

The aim is to complete both facilities by 2021, several years earlier than previous forecasts and using innovation in areas such as waste packaging to reduce costs. 

An estimated 1,500 tonnes of radioactive waste was consigned to the two facilities between 1957 and 1998. 

Radiation levels are too high for man entry to either facility, so robotic equipment will be used to retrieve, analyse, shred and package the waste. 

Separate headworks and waste processing facilities will be built above each facility. 

A 60-strong team is now working on the project, with employment levels expected to peak at about 200 during the construction phase in 2013-16. 

The project team is looking wherever possible to use technology already proven elsewhere such as remote vehicles, cranes, shredders, remotely operated grabs, water treatment, analysis and monitoring. 

They will solidify the processed waste in a type of container that is new to Dounreay but proven by the nuclear industry in other parts of the world. 

The use of boxes made from steel, lead and concrete will provide shielding from harmful radiation and remove the need to build a heavily shielded store for the previous design of containers. This will save tens of millions of pounds in design and build costs. 

About 20 companies are likely to be involved in contracts ranging from the design and build of mechanical systems such as cranes to the procurement of robotics capable of operating in high radiation zones, major construction, plant decommissioning and back-filling of the shaft and silo. 

The project is being managed for the NDA by Dounreay Site Restoration Ltd, the site licence company acquired by BDP. 

Project director Bo Wier said: "Emptying the shaft and silo at Dounreay is one of the biggest clean-up challenges in Europe and one of the priorities for the NDA in the UK. 

"We believe we can deliver the decommissioning on an earlier timescale and at lower cost than previously thought by combining proven, off-the-shelf technology with innovation in design. 

"By 2021, we aim to have all the waste safely packaged for long-term storage above ground and both facilities left in a condition that do not pose a hazard to future generations. This is significantly earlier than previous estimates and offers substantial cost savings to the NDA." 

DSRL put the plans on display in neighbouring village Reay and in the Thurso information office during September, to seek feedback from the community, before making a formal application to the Highland Council at the end of October. 

Subject to consent, construction is scheduled to begin in the second half of 2013 and take up to three years. Once emptied, both facilities will then be back-filled. 

Shaft used for waste 

The shaft was sunk to enable the building of a tunnel, through which low-active radioactive effluent would be discharged. The shaft was used to transfer excavation equipment in and out of the tunnel, for removing spoil and for pumping out groundwater. 

A concrete plug separates the tunnel from the shaft, which is mostly unlined. 

In 1958, the shaft was licensed to take radioactive waste and was routinely used for unconditioned intermediate level waste. 

The wet silo - an engineered, concrete-lined bunker - was brought into use as an ILW store in 1971 to allow the shaft to be taken out of routine service. 

All consignments to the shaft halted in 1977 following an explosion. 

A decision to empty both facilities was taken by the UK Government in 1998. 

To prevent groundwater seeping in as waste is retrieved, and becoming contaminated, the surrounding rock was grouted. 

Specialist grout from Sweden was ground down until it was finer than toothpaste, injected through boreholes and squeezed into the fissures around the shaft where it hardened. 

The project, completed in 2008, won a number of industry awards. Further work was carried out to prepare for the retrievals phase.